I was looking at your website. Found it very informative. But I have some crepe myrtles that the leaves turn brown then fall of. I live in the high desert of California and the get watered every other day. Thank you for your help.
Crepe Myrtles in High Desert
Certified GKH Gardening Expert
It may be caused by a fungus or pests. I would recommend treating the tree with a fungicide and a pesticide. Neem oil is a good organic solution as it is both a fungicide and a pesticide and is systemic, so it will treat the whole tree even if you can't reach the whole tree.